The present invention relates generally to die casting machines, and specifically to such a machine made with a one piece frame for supporting the dies as well as the pressurized die clamping mechanism.
Die casting dies are used for making die castings and are usually composed of two structures that can be moved relative to each other to create the shape of a casting enclosed between them. Also, dies can be moved relative to the casting to enable removal of the casting upon formation. However, in some cases a casting cannot be formed using only two casting members, and an additional component is required, known as a core slide. The structure of the core slide, which includes a hydraulic core pulling cylinder, often extends beyond the "die space" and actually beyond the exterior dimensions of the die casting machine.
Die casting machines typically have long working lives, and this certainly applies to such machines manufactured by the Lester Engineering Company of Cleveland, Ohio. These so-called Lester machines, which are disclosed in U.S. Pat. No. 2,411,999, include an upper frame which is a one piece casting. The upper frame provides structural support for the hydraulic toggle mechanism which clamps the two dies together, as well as providing support for the dies themselves.
Originally built in the 1940's, the Lester machines established a reputation for durability and reliable operation due in part to the strong upper frame. The one piece upper frame construction not only provides substantial support for the 600,000 pounds of pressure generated by the clamping mechanism, but also maintains the alignment of the dies for higher quality castings.
Despite the advantages of Lester machines, their main advantage, the solid frame, is also their main disadvantage in the modern factory environment, especially where Just-In-Time manufacturing strategies are used. At the time the Lester machine was designed, operators would typically run a set of dies for a relatively long period of time between die changeovers. Thus, the time involved to make die changeovers was not considered a significant factor affecting manufacturing efficiency. In contrast, many modern factories need to change their dies on a more frequent basis, and in some cases several changes a day are required.
For dies which have several side core pulling cylinders, changeover in a Lester machine is a tedious process. This is because the side core pulling cylinders project beyond the fixed frame members in several directions. As such, the cylinders and dies cannot be removed as a unit without the cylinders becoming hung up on the frame. Thus, in the Lester machines, each time a die change must be performed, the core pulling cylinders must be disassembled before the dies can be pulled from the frame. Such die changes can take as long as 8 to 12 hours to complete.
Another disadvantage of dismantling the die set is that adjustments are often required to the core slide after it has been reassembled to the die to ensure that the castings produced are dimensionally correct. This adjustment is performed after at least one casting is made and measured. These adjustments further extend the time that a die casting machine is out of production for a die change.
More modern die casting machines have upper frames with movable rod-like upper frame members which slide linearly under either manual or automatic control away from the die area to permit the dies and core pulling cylinders to be removed as a unit. A major advantage of these more modern machines is that the replacement die set can be fully assembled prior to the change and be waiting at the machine for the removal of the previous die set. However, and keeping in mind the major advantage of the Lester machines with their solid frame, a significant design and operational problem of more modern die casting machines is that the newer frames must be specially built so that the movable frame members can be secured against the substantial clamping forces necessary in the die casting process, while maintaining accurate alignment of the dies. These modern frames are inherently less rigid than the Lester machines, and are consequently less accurate than the one piece frame type machines.
Accordingly, it is a principal object of the present invention to provide a modification for a one piece frame die casting machine which permits rapid changeovers of die sets having multiple core pulling cylinders.
Another object of the present invention is to provide a modification for a Lester type die casting machine which permits the temporary displacement of at least one frame member to permit the rapid exchange of die sets without requiring disassembly of the core pulling cylinders.
Yet another object of the present invention is to provide a mechanism for a Lester type die casting machine which accurately locates a displaceable frame member in position on the frame after exchange of die sets, and which also securely retains the frame member to the frame to withstand the significant clamping forces without causing misalignment of the dies.
Still another object of the present invention is to provide a mechanism for the conversion of a one piece frame type of die casting machine to permit rapid changes of die sets complete with core pulling cylinders, at a fraction of the cost of replacing the existing machine with a new die casting machine.